This invention relates to lightwave devices and more particularly to a subassembly used in packaging optoelectronic devices such as photodiodes and light emitting diodes (LEDs).
Conventional packages for discrete optoelectronic devices typically are made out of a variety of dissimilar materials, such as metal, glass and ceramic, and involve relatively complicated manipulation of components during assembly. U.S. Pat. Nos. 4,357,072 (LED), 4,119,363 (laser) and 4,233,619 (photodetector) are illustrative. Assembly involves manipulating components in three dimensions in order to place the components in the desired locations; for example, alignment of a device to a substrate, alignment of a fiber to a ferrule, alignment of a ferrule to a package, and finally alignment of the package to the device. These alignment steps depend upon fairly specialized, expensive equipment. In general, therefore, z-axis assembly is not possible in those designs; that is, one cannot simply move the components along a z-axis perpendicular to the substrate and place them on the substrate without further orientation being required in the x-y plane. In addition, because the packages include dissimilar materials, great care is required to insure that the thermal-expansion coefficients are adjusted in such a way that the alignments are stable even though the ambient temperature changes. Instability, of course, leads to mechanical movement of the components and consequently to a decrease in optical coupling between, for example, the device and the fiber. Often this situation leads package designers to compromise between thermal sinking and stability criteria. At the very least, it increases cost.
For many expensive applications, notably long haul transmission systems, the relatively high cost of manufacturing such packages can be tolerated. However, for some cost sensitive, high volume applications, such as lightwave systems between central switching offices or remote-terminals and subscribers' homes (known as the subscriber loop), the high cost of such packages renders them unsuitable.
Thus, it would be desirable to have a packaging scheme which (1) uses, as much as possible, commercially available equipment for the production of the pieceparts, for the alignment of the parts, and for closing of the package; and (2) accommodates different size packages for different applications without requiring extensive retooling or new assembly techniques. For example, it would be desirable, on the one hand, to have a subassembly which fits inside of a dual-in-line package (DIP) header and is adapted to a 125 .mu.m diameter fiber and, on the other hand, to have a different subassembly which is adapted to a larger diameter fiber and is surface mounted on a printed circuit (PC) board. Normally, the fabrication of these two designs would require retooling which is undesirable for reasons of cost and commonality.